Practice Point: The reported association between fluoride in water and lower IQ scores doesn’t apply at the levels recommended by American dental and medical organizations.
EBM Pearl: Consistent findings in multiple subgroup analyses, especially separate analysis including only studies with the lowest risk of bias, offers reassurance that results of a systematic review of observational studies are trustworthy.
Balancing risks and benefits makes up a lot of what we do in clinical medicine. But this equation works best when we have a full and accurate representation of the risks and benefits. In fact, it requires it. In the case of water fluoridation, it’s possible that much of the discussion of its risks and benefits has not been fully informed or updated with new information.
Water fluoridation was first introduced in the United States in the 1950s as a public health intervention to decrease dental caries. Currently, about 70 percent of United States communities have fluoridation, with some choosing to ban it for a variety of reasons. The argument in the 1950s was that fluoridation led to a 60 percent reduction in dental caries. Over time, later studies found smaller and smaller benefits. Is this yet another example of the old adage: “use new drugs quickly while they still work”?
Well, it’s complicated.
Since the 1950s, fluoride toothpastes, dental sealants, and pediatrician-applied fluoride during well-child checks for preschoolers have all become commonplace. This was reflected in a 2024 Cochrane review of water fluoridation that found an absolute decrease in dental caries on average of about two teeth per child in studies published before 1975 and one-quarter tooth per child in studies published more recently. It’s important to note that the children most likely to benefit from water fluoridation are those without access to other modalities for proper oral health, and so there may be a health equity component to water fluoridation that should be kept in mind.
So, if the benefit of water fluoridation is smaller than it used to be, what about the risks?
Dental fluorosis is a well-known problem and is directly related to exposure to too much fluoride. At water fluoridation levels of 0.7 parts per million (PPM), which is the current recommended level in the United States, aesthetically significant fluorosis is estimated to be about 10 percent. Of greater concern is data from a recent systematic review that reported an inverse relationship between fluoride exposure and IQ scores in children. This systematic review published in JAMA Pediatrics evaluated 74 observational studies; 45 were conducted in China, and 52 were considered to be at high risk of bias. In a subgroup analysis of 59 studies that evaluated fluoride specifically in drinking water, a dose-dependent association between fluoride exposure and lower IQ scores in children was found, but only when studies of fluoride concentrations above 1.5 PPM were included. When the analysis included only studies with < 1.5 PPM, there was no association between fluoride level and lower IQ scores.
There are many limitations of this study, but two noteworthy pitfalls are: 1) most of the studies were deemed to have a high risk of bias (with concern for bias above and beyond that which is inherent to observational studies), and 2) there was evidence of publication bias, suggesting that there may have been studies finding no association between fluoridation and IQ scores that were never published. Also, extraneous sources of topical fluoride, such as those provided at well-child and dental visits as well as fluoride sources in diet may confound the ability to draw strong conclusions about the risks associated with water fluoridation and its impact on dental caries.
This systematic review made for exciting headlines, but the bottom line seems to be that while water fluoride levels below 1.5 PPM do not pose a risk to IQ scores, there may be some risk at higher concentrations. In the United States in particular, water fluoridation still seems to be a low-risk intervention. However, the benefit to dental health is also much smaller than once thought. All told, a recalibration of the scales may be in order when discussing the potential risks and benefits of water fluoridation at both the patient- and population-health levels.
For more information, see the topic Dental Caries in DynaMedex.
Reference: JAMA Pediatr 2025 Jan 6 early online
